Function chain

pub fn chain<A: IntoIterator, B: IntoIterator<Item = A::Item>>(
    a: A,
    b: B,
) -> Chain<A::IntoIter, B::IntoIter> 

Chain two iterators together. The result first iterates over a, then b, until both are exhausted.

This addresses a quirk where deep iterators would not be optimized to their full potential. Here, functions are marked with #[inline(always)] to indicate that the compiler should try hard to inline the iterators.